Ferrofluidic seals are currently used in a broad variety of products. Millions have been installed in Winchester drives, and thousand are used in a variety of vacuum feedthroughs. Despite the maturity of the technology, it is well recognized that these seals suffer from some disadvantages. These shortcomings can be traced mostly to the nature and stability of the ferrofluids themselves.
Ferrofluids are chemically stabilized colloids. As such their stability depends on the chemical stability of the carriers, surfactants and dispersants used each separately and as a suspension medium for the ferromagnetic particles. While this technology is proprietary it is well known that the life of most versatile ferrofluids is limited by the deterioration of their chemistries.
Furthermore, most ferrofluids have an additional major deficiency, namely, their dynamic range of operation. This is due to the fact that in the majority of carriers the viscosity rapidly decreases with increasing temperature, thus a seal designed for a given rotation rate cannot be operated at much higher rotation rates. Despite the maturity of the technology, ferrofluids based on silicones are still not available, yet silicone carriers are superior to existing technology in a number of applications where weak dependence of viscosity on temperature and where large operating temperature intervals including cryogenic ranges are called for.
To remedy most of these shortcomings I have invented a new family of colloidal systems in which colloidization is established by pure physical means. These colloids which we have called "Diamagnetic Colloids" or "Diocols" have been described in a copending application Ser. No. 07/281,832 entitled "Diamagnetic Colloids Containing Superconducting Particles" and have the unique property that they can be positioned and moved in magnetic fields by means that can be termed opposite to those used with ferrofluids. Specifically, while ferrofluids seek magnetic field flux maxima, diamagnetic colloids seek magnetic field minima.
The design of diamagnetic colloids based seals is thus reduced to the proper choice of the carrier fluid, the superconducting particles that are suspended in that carrier fluid and the design of magnetic field circuits possessing topologies with minima where the seal is to be formed.